Last updated on June 11th, 2021
Immunity is defined as the resistance offered by the host against microorganisms or any other foreign substance(s). Immunity can be broadly classified into two types:
- Innate Immunity-present right from the birth
- Acquired/Adaptive Immunity- acquired during the course of life.
The innate immune system recognizes molecular structures that are unique to microbes called pathogen-associated molecular patterns (PAMPs) via pattern recognition receptors (PRR). The innate immune system aims to eliminate microbes and other foreign particles using:
- Physical barriers
- Proteins (complement)
- Cells (phagocytosis, cytotoxic killing).
But many pathogens can breach/resist the innate immune system. To clear such pathogens specific and more robust adaptive immunity comes into play. There are two types of adaptive immune response, humoral immunity (where products of B-cells (precisely plasma cells) i.e. antibodies bind with specific extracellular antigens and cells mediated immunity, whereas T cells (precisely Cytotoxic T Cells) kills both intracellular antigen and altered self cells. T helper cells help in humoral immunity.
Some of the major differences between Innate Immunity and Adaptive Immunity is summarized in the table below (To give different perspectives, I have made this table a bit lengthy, some properties may look similar thus can be grouped at your convenience):
|Innate Immunity||Adaptive/Acquired Immunity|
|Definition||Innate immunity is the inborn resistance against infections that an individual possesses right from birth, due to his genetic or constitutional markup.||Acquired immunity is the resistance against infecting foreign substances that an individual acquires or adapts during the course of life.|
|Origin||Prior exposure to the antigen is not required. It is present before the first exposure to microbial antigen.||Develops during lifetime following the antigenic exposure|
|Activity||Always present||Normally silent but triggers often exposure to pathogens|
|Diversity||Diversity is limited; It is active only against a limited repertoire of antigens.||Adaptive immunity is more varied and involves specialized immune responses.|
|Specificity||Non-specific defends against any pathogen upon first exposure||Antigen specific-responds to specific pathogen on 2nd or latter exposure|
|Functional against||General microbes (bacteria, fungi, parasites), etc, Chemical irritants, burns, tissue injury, etc.||Microbes, as well as nonmicrobial substance, called antigen|
|Response time||Immune response occurs in minutes||Takes days to generate immune response|
|Potency||It has a limited and lower potency||It has highly potent immune response|
|Target Antigens||Innate immunity develops against antigens that are shared by many microbes (called pathogens-associated molecular patterns).||Acquired immunity develops against antigens that are specific for each microbe.|
|Host Cell Receptors||Host cell receptors of innate immunity (called pattern recognition receptors) are non-specific, e.g. Toll-like receptor||Host cell receptors are specific, e.g. T cell receptor and B cell immunoglobulin receptor.|
|Immunological Memory||Absent |
It reacts with equal potency upon repeated exposure to same pathogen.
Presence of memory cells triggers a faster and potent response when re-exposed to same pathogen.
|Heritance||Innate immunity is inheritable||Passive acquired immunity is heritable from mother to neonates for a brief period after birth.|